Microwave dielectric heating of drops in microfluidic devices

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"Microwave dielectric heating of drops in microfluidic devices"
David Issadore, Katherine J. Humphry, Keith A. Brown, Lori Sandberg, David A. Weitz, and Robert M. Westervelt
Lab on a Chip Online advance article (2009)

Soft Matter Keywords

microfluidic, emulsion, dielectric heating

Figure 1. (a) Schematic of the microfluidic microwave heating system. (b) Microfluidic drop maker. Water drops in fluorocarbon oil are being produced. (c) Parallel drop splitters reduce drops to 63% of their original diameter. (d) Section of microfluidic channel between heating electrodes. The white circles are drops flowing in oil between the two dark metallic electrodes. (e) Image of the actual device as set up on the fluorescence microscope.
Figure 2. (a) Long time fluorescence exposure overlaid onto bright field image of the heating region. A decrease in fluorescence signal from the cadmium selenide nanocrystals indicates an increase in temperature. (b) Line average of the normalized fluorescence intensity versus horizontal position. (c) Change in drop temperature versus time, calculated from (b) and a calibration curve.
Figure 3. (a) Steady state increase in temperature as a function of microwave power, determined from inset plot of temperature change versus time for multiple microwave powers. (b) Log-linear plot of scaled inset data, showing that the drop temperature change has a single time constant.



Practical Application of Research

The research begins to open up the possibility of localized temperature control in microfluidic systems. Most systems to date have spatial control down to a few centimeters, but this work pushes temperature control to the 100s of microns scale. The heating and cooling of the water droplets occurs on timescales much shorter than previously accessible. With temperature changes of nearly 30 degrees above ambient achievable, the microwave heating paradigm can be applied to biologically relevant systems, including PCR reactions for DNA analysis, as well as protein denaturing studies and enzyme optimization. Combining this rapid heating with the high-throughput capabilities of microfluidic emulsions has the potential to allow researchers to analyze large sample populations of temperature sensitive reactions.

Dielectric Heating of Water Drops On-Chip


written by Donald Aubrecht